Articles comprising magnetically soft thin films

ABSTRACT

The invention is embodied in a soft magnetic thin film article comprising an iron--chromium-nitrogen (Fe--Cr--N) based alloy and methods for making such article. The soft magnetic thin film article is formed using an iron--chromium--nitrogen based alloy with tantalum in one embodiment and with at least one of the elements titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), molybdenum (Mo), niobium (Nb) or tungsten (W) in another embodiment. The article is formed such that the alloy has a relatively high saturation magnetization (e.g., greater than approximately 15 kG) and a relatively low coercivity (e.g., less than approximately 2.0 oersteds) in an as-deposited condition or, alternatively, with a very low temperature treatment (e.g., below approximately 150° C.). The inventive films are suitable for use in electromagnetic devices, for example, in microtransformer cores, inductor cores and in magnetic read-write heads.

This is a division of application Ser. No. 08/595,543 filed Feb. 2,1996, now U.S. Pat. No. 5,780,175.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to thin films of magnetically soft alloys. Moreparticularly, the invention relates to articles comprising these alloys.

2. Description of the Related Art

Soft magnetic thin films are useful in modern, high-frequency,electromagnetic devices as a field-amplifying component, e.g., in theread-write head for magnetic disk memories in computers or as a core inmicrotransformers and inductors. Among the desired properties of thesefilms are relatively high saturation magnetization (4πM_(s)), lowcoercivity (H_(c)), high permeability, high electrical resistivity andcorrosion resistance. Various applications of soft magnetic thin filmsare described, for example, in books Magnetic Thin Films by R. F.Soohoo, Harper and Row, 1965; Thin Ferromagnetic Films by M. Prutton,Butterworth, 1964; and in articles C. R. Sullivan and S. R. Sanders,IEEE Trans. on Power Electronics, Proc. 24th Annual Power ElectronicsSpecialists Conf., p. 33-40, June 1993; and T. Yachi et al., IEEE Trans.Magn. 28, 1969-1973 (1992).

Among the known soft magnetic thin films, nickel--iron (Ni--Fe) basedfilms such as 80% Ni-20% Fe (permalloy) are used most widely because ofexcellent magnetic properties and zero magnetostriction characteristics.Fe-based films such as iron--tantalum (Fe--Ta), iron--zirconium (Fe--Zr)and iron--hafnium (Fe--Hf) alloys generally exhibit higher saturationmagnetization of 15-20 kilogauss (kG) as compared to about 10 kG for the80% Ni permalloy films (see, e.g., N. Kataoka et al., Japanese J. Appl.Phys. 28, L462-L464, 1989, Trans. Jap. Inst. Metals 31, 429, 1990),however, they exhibit poorer soft magnetic properties and requirepost-deposition heat treatment.

To obtain improved soft magnetic properties, nitrogen-containing filmsof these Fe-based alloys such as iron--tantalum--nitrogen (Fe--Ta--N)have been prepared. See, for example, E. Haftek et al., IEEE Trans.Magn. 30, 3915-3917 (1994); N. Ishiwata et al., J. Appl. Phys. 69, 5616(1991); J. Lin et al., IEEE Trans. Magn. 30, 3912-3914 (1994); and G.Qiu et al., J. Appl. Phys. 73, 6573 (1993). However, although desirablemagnetic softness with a coercivity, H_(c), of less than approximately 2oersted (Oe), which is desirable for microtransformer applications, isobtainable in these nitrogen-containing films, it is apparent from theaforementioned articles that such desirable soft magnetic properties aredifficult to obtain in the as-deposited films, but are possible afterpost-deposition heat treatment at high temperatures.

However, such heat treatment of deposited films is an additionalprocessing step that needs to be avoided if possible, not only from themanufacturing cost point of view but also because of the complicationsof having to expose to high temperature various other components andmaterials in the devices. As a result of high temperature exposure, someof these components can be damaged, e.g., decomposition of polymers orpolyimide insulating films, diffusion-induced chemical changes ordamages, stress problems caused by thermal expansion mismatch ofdifferent materials.

Therefore, it is desirable for the required soft magnetic properties inthe films to be obtained in the as-deposited condition, or at the worst,with a very low temperature heat treatment below approximately 150° C.where damage to polymers such as polyimide is kept relatively low. Thisapplication discloses new soft magnetic films with such desirablecharacteristics. Also, it is desirable to improve thecorrosion/oxidation resistance of the Fe-rich thin films, as the oxidesof iron and iron-rich alloys generally exhibit substantially reducedmagnetic saturation. This application discloses thin films with improvedcorrosion resistance.

SUMMARY OF THE INVENTION

The invention is embodied in a soft magnetic thin film articlecomprising an iron--chromium--nitrogen (Fe--Cr--N) based alloy with atleast one of the elements titanium (Ti), zirconium (Zr), hafnium (Hf),vanadium (V), molybdenum (Mo), niobium (Nb) or tungsten (W) in anotherembodiment. The article is formed such that the alloy has a relativelyhigh saturation magnetization (e.g., greater than approximately 15 kG)and a relatively low coercivity (e.g., less than approximately 2.0oersteds) in an as-deposited condition or, alternatively, with a verylow temperature treatment (e.g., below approximately 150° C.). Theinventive films are suitable for use in electromagnetic devices, forexample, in microtransformer cores, inductor cores and in magneticread-write heads.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing one method for making the Fe--Cr--Nbased soft magnetic thin films according to the invention;

FIGS. 2a-c are schematic diagrams showing a thin film depositionconfiguration in the presence of applied magnetic field;

FIG. 3 is a magnetic hysteresis (M-H) loop of an as-depositedFe--Cr--Hf--N alloy film (approximately 1000 Å thick) along the easydirection of magnetization according to another embodiment of theinvention;

FIGS. 4a-b are schematic diagrams showing the structure of a pot-coretype microtransformer comprising the inventive Fe--Cr--N based films;

FIGS. 5a-b are schematic diagrams showing the structure of a toroid typemicrotransformer comprising the inventive Fe--Cr--N based films; and

FIGS. 6a-b are schematic diagrams showing the structure of a magneticrecording head comprising the inventive Fe--Cr--N based films.

It is to be understood that the drawings are to illustrate the conceptsof the invention and are not to scale.

DETAILED DESCRIPTION

Referring to the drawings, FIG. 1 is a block diagram showing one of themethods for making the Fe--Cr--N based soft magnetic thin films inaccordance with the invention (i.e., soft magnetic thin films comprisingFe, Cr, N and at least one of the following elements: Ti, Zr, Hf, V, Mo,Nb or W). A first step 110 is to provide an alloy target or targets fromwhich the magnetic thin films of the invention are to be deposited,e.g., via chemical deposition or via physical deposition such assputtering, evaporation, molecular beam epitaxial growth, ion beamdeposition and laser ablation.

For example, deposition by sputtering is amenable to large-scaleindustrial manufacturing. The sputtering target (shown as 210 in FIG.2a), which is typically in the form of a round plate, has, in oneembodiment, the alloy composition similar to the desired filmcomposition and has, in another embodiment, composite sections ofdifferent metals or alloys on the target surface to be sputtered away.Alternatively, the film deposition is accomplished by using multipletargets, e.g., by co-sputtering from two or more targets with differentcomposition chosen so that the final composition of the deposited filmon the substrate corresponds to the desired composition. For example, indata shown in FIGS. 3 and 4, co-sputtering with two targets (e.g., aFe-5.3% Cr target on one side and a Hf target on the other sideseparated by approximately 6 inches) was utilized.

In another embodiment, diode sputtering or triode sputtering is used fordeposition of the inventive films. Of these, triode sputtering generallyis preferred because it uses lower bias voltage and lower Ar pressure,thus allowing easier control of the sputter deposition and the formationof desired nanocrystalline microstructure in the inventive Fe--Cr--Nbased soft magnetic films.

In an embodiment of the present invention, nitrogen is incorporated intothe alloy film by reactive deposition, i.e., by continuously supplying aspecific partial pressure of nitrogen gas in the background Ar gascarrier during the sputtering process. We currently believe that thenitrogen atoms go into the thin film structure both by reaction with oneor more of the metallic elements in the form of nitride, such asCr-nitride, Fe-nitride, or a nitride of the remaining element Ti, Zr,Hf, V, Mo, Nb or W, and by dissolution in the form of interstitialsolute atoms in the alloy crystal lattice. In another embodiment,instead of reactive sputtering, nitrogen is supplied by alloying itdirectly into the sputtering targets. Alternatively, nitrogen is addedto the films after deposition, e.g., by ion implantation. In thismanner, thin films of inventive alloys, prepared by any suitabletechnique, are subjected to nitrogen implantation with appropriate dosesand processing temperatures.

In the case of using a single alloy target for sputtering, the desiredcomposition of the target for the inventive film deposition is: Febalance, Cr in the range of approximately 0.5-20.0 atomic %, preferably1.0-12.0% and even more preferably 2.0-8.0 atomic %, and the remainingelement in the range of approximately 0.1-10.0 atomic %, preferably0.1-5.0%, and even more preferably 0.1-3.0%. According to an embodimentof the invention the remaining element comprises one or more elementschosen from Ti, Zr, Hf, V, Mo, Nb and W. If the nitrogen atoms areincorporated in the target, the desired composition is 1.0-30.0 atomic%, preferably 2.0-20.0%, even more preferably 2.0-15.0%. If nitrogen isto be added by reactive sputtering, the alloy target has 0.0-20.0%nitrogen depending on the concentration of the nitrogen gas used duringthe sputtering.

The next step 120 is to provide a substrate onto which the inventivemagnetic film is to be deposited. A clean and smooth non-magneticsubstrate surface is desired for microtransformer-type applications.Desirable substrate materials include, e.g., semiconductors such assilicon (Si) and gallium--arsenide (Ga--As), and other materials such asglass, quartz, ceramics, polymers and polyimide. A silicon substrate isconvenient if other semiconductor electronic IC circuitry andinterconnection features are to be integrated on portions of the samesubstrate. The IC circuits may be fabricated either before or after thedeposition of the magnetic films.

In the case of microtransformer or inductor applications, especially forhigh frequency devices (e.g., f=1-1000 MHz), the inventive Fe--Cr--Nbased thin films are formed, in one embodiment, into a multilayer,patterned configuration with dielectric spacer layers, such asspin-coated or spray-coated and optionally photolithographicallypatterned polyimide films, interleaved therebetween. This multilayerconfiguration of magnetic thin films is desirable to provide highelectrical resistance for each film layer so as to minimize eddy currentloss on high frequency operation.

In this multilayer arrangement, more than one substrate material isinvolved, e.g., the first substrate is Si and then after the depositionof the first Fe--Cr--N based magnetic layer and polyimide insulationlayer, the polyimide becomes the next substrate for the remaining layersof magnetic materials. As the magnetic properties of alloys andcompounds are influenced often by crystallographic texture and latticeparameters, the substrate material is chosen, if desired, to provideepitaxial growth with accompanying lattice parameter modifications, toinduce growth texture (such as a columnar structure), or to inducedesired degrees of crystallization.

The next step 130 is to perform a deposition of Fe--Cr--N based thinfilms, e.g., by reactive sputtering in a nitrogen-containing atmosphere.The desirable amount of nitrogen is in the range of 0.2-30.0% in volumein argon (Ar) and preferably 0.5-10.0% in volume with a total (Ar+N₂)gas pressure of 10⁻² to 10⁻⁴ Torr. The sputtering target(s) aredesirably subjected to a bias voltage in the range of approximately20-500 volts, preferably 50-200 volts.

For microtransformer or inductor applications involving multilayerdeposition and temperature-sensitive dielectric spacer layers such aspolyimide, the substrate temperature is kept preferably at or nearambient temperature. Alternatively, the substrate temperature is keptbelow approximately 150° C. (above which many polymers or polyimidebegin to get damaged with undesirable chemical or structural changes).For other device applications in which temperature-degradable materialsare not involved, higher substrate temperatures can be used.

Another embodiment of the present invention uses one or more magneticfields during the deposition of the Fe--Cr--N based films to inducemagnetic anisotropy in the desired direction. Since the inventive filmshave soft magnetic properties, a relatively low field is applied tointroduce preferential ordering of atoms to form an easy direction ofmagnetization for higher permeability, lower coercivity, and more squareM-H loop shape. The desired magnitude of applied field is in the rangeof approximately 2-5000 Oe, preferably in the range of approximately10-500 Oe. Since the preferred deposition temperature for the inventivefilms is near ambient temperature, the field is applied conveniently byplacing one or more electromagnets or permanent magnets near thesubstrate without fear of solenoid wire insulation damage or loss ofmagnetism in permanent magnets upon heating toward or above the Curietemperature.

In the case of magnetron sputtering, the stray magnet field itself inthe deposition system is used conveniently to induce anisotropy. Asshown in FIGS. 2a-c, if an additional field is to be applied, the use ofone or more permanent magnets is particularly desirable because of thesimplicity of placing magnets either on the sides of or underneath thesubstrate 220 during the deposition. Various permanent magnets 240 areacceptable, including the high coercivity materials samarium--cobalt(Sm--Co), neodymium--iron--boron (Nd--Fe--B), barium--ferrite andiron--chromium--cobalt (Fe--Cr--Co), which allow self-demagnetization tobe reduced in small or short magnet configurations. Multiple magnetarrays, such as shown in FIG. 2(b), provide a stronger field to thesubstrate regions between the magnets than the case of FIG. 2(a). Also,the magnet arrangement shown in FIG. 2(c) induces vertical anisotropy inthe film.

In the case of multilayer deposition, the thickness of the eachFe--Cr--N based layer is typically in the range of approximately0.001-10.0 microns, preferably in the range of 0.01-2.0 microns. Higherfrequency operations generally require thinner magnetic films to reduceeddy current loss. The insulating (dielectric) spacers such as aluminumoxide or polyimide between the magnetic layers are typically in therange of approximately 0.001-1.0 μm. The desired number of magneticlayers depends on the total amount of magnetic flux required and thethickness of each layer, but is typically between 1-1000 layers.

According to an embodiment of the invention the composition of theinventive film includes: Fe balance; Cr typically in the range ofapproximately 0.5-20.0 atomic %, preferably in the range of 1.0-15.0atomic % and even more preferably in the range of 2.0-10.0 atomic %; Nin the range of approximately 1.0-30.0 atomic %, preferably in the rangeof 2.0-20.0 atomic %, even more preferably in the range of 2.0-15.0atomic %; and the remaining element, chosen from Ti, Zr, Hf, V, Mo, Nbor W, in the range of approximately 0.1-10 atomic %, preferably in therange of 0.1-6.0 atomic %, and even more preferably in the range of0.1-3.0 atomic %. Also, other metallic elements such as transitionmetals, e.g., nickel (Ni), and cobalt (Co), rare earth metals, e.g.,cerium (Ce), yitrium (Y) and lanthanum (La), or other elements, e.g.,carbon (C), aluminum (Al) and silicon (Si), may be present as impuritiesin a total amount less than approximately 2 atomic %, preferably lessthan approximately 0.5 atomic %.

Structurally, the inventive film includes a nanocrystalline structurewith the average crystallite size (grain-size) of less thanapproximately 1000 Å, preferably less than approximately 500 Å, and evenmore preferably less than approximately 200 Å. Also, the inventive filmexhibits excellent soft magnetic properties in the as-depositedcondition without having to go through post-deposition heat treatment.The coercivity (H_(c)) is typically less than approximately 5 Oe,preferably below approximately 2 Oe, and the saturation (4πM_(s)) istypically greater than approximately 10 kG, preferably greater thanapproximately 15 kG, and even more preferably greater than approximately18 kG. Some of the processing and properties of the inventive films aredescribed in the examples given below.

Thin films of the Fe--Cr--Hf--N alloy were deposited on 4 inch diameter(100) Si substrates by triode DC magnetron sputtering using aco-sputtering process with two 2.25 inch diameter targets of Fe-5.3% Cr(in atomic %) and pure Hf, or Fe-8.5% Cr and Hf, and using a reactiveprocess in a nitrogen-containing atmosphere. The sputtering chamber wasfirst pumped down to 2×10⁻⁷ Torr, and then the reactive sputtering wascarried out under gas atmosphere with Ar+N₂ initial pressure of about5×10⁻³ Torr, and the gas flow rate of 50 standard cubic centimeters perminute. The amount of nitrogen in the argon gas was either 0, 2%, 3.5%or 5% in volume. A bias voltage of 140V was applied to the Fe--Cr targetand 60V for the Hf target. The Si substrate was kept at ambienttemperature during sputtering. The rate of sputter deposited was about15 Å/minute. The films were 1000-2000 Å thick.

The M-H loops were measured by using a Vibrating Sample Magnetomer (VSM)in conjunction with Helmholtz magnetizing coil. The loops were measuredas a function of in-plane orientation in order to determine thedirection of easy and hard magnetization. Because of the co-sputteringprocess from the two targets placed approximately 6 inches apart, thedeposited Fe--Cr--Hf--N films have a concentration gradient from one endto another, i.e., the Fe--Cr rich end and the Hf rich end. Smallsamples, each about 0.125 inch square, were cut from various locationsof the substrate to represent a spectrum of the gradient composition. Asample with an approximate composition of Fe-4.3 atomic % Cr-0.3%Hf-5.3% N and a thickness of approximately 1000 Å gave the followingmagnetic properties: 4πM_(s) =17.2 kG and H_(c) =1.8 Oe. Also, see FIG.3.

As is evident from Example 1, excellent soft magnetic properties areobtained in the as-deposited condition of the inventive films of bothembodiments. Such combinations of high 4πM_(s) and low coercivity arevery attractive for use in many electromagnetic devices, such asmicrotransformers and recording heads. The easy axis M-H loop of thefilms are shown in FIG. 3. The square nature of the M-H loops areevident.

The addition of Cr to a Fe--x--N alloy film (where x is Ta or at leastone of the elements Ti, Zr, Hf, V, Mo, Nb or W) makes it possible toachieve improved soft magnetic properties (low H_(c) and square M-Hloop) in the as-deposited condition, and eliminates the need forpost-deposition heat-treatment. The exact reason why Cr induces suchcharacteristics is not understood at the moment, but it could be relatedpossibly to the ease of formation of a desirable nanocrystallinemicrostructure or the reduction of undesirable magnetostriction in theas-deposited films.

Also, because of the presence of Cr, the inventive films exhibitsubstantially improved (at least 30%) resistance to corrosion/oxidationas compared to the prior art soft magnetic films without Cr. Forexample, films approximately 1000 Å thick and having a composition ofFe-6.3% Cr-3.2% Ta-16.1% N on a Si substrate were kept in tap water or50% nitric acid for 30 minutes. There was no noticeable corrosion ordissolution of the thin film material in either case. Also, there was nodiscoloration or decrease in film thickness, and there was no measurablechange in total magnetic moment. Furthermore, the H_(c) and the"squareness" of the M-H loop also did not change. The resistance tooxidation is important in maintaining the soft magnetic propertiesduring actual device usage, as the oxidation of Fe-rich alloys causeschanges toward lower 4πM_(s), higher coercivity and inferiorpermeability.

In an alternative embodiment, the inventive films are given an optionallow-temperature heat treatment, if desired, to further improve the softmagnetic properties. In order to reduce the damage to insulating layerssuch as polyimide, low heat treating temperatures below approximately150° C. are used. In order to minimize surface oxidation during the heattreatment, a high vacuum atmosphere (e.g., better than approximately10⁻⁴ Torr) is used. A lower vacuum is used if the top surface of thefilm of film layers is protected, e.g., by oxidation-resistant coatingssuch as Cr, Al, oxide, or nitride films.

According to an alternative embodiment of the invention, the film isformed as a composite structure with a different type of magnetic layer.For example, the composite structure has one or more exchange biasfilms, which are antiferromagnetic, ferromagnetic or ferrimagnetic,added directly on the soft magnetic film surface. Specifically, a thinfilm of Fe-50% manganese antiferromagnetic alloy is added onto some orall of the Fe--Cr--N based soft magnetic layers to shift the M-H loop(by more than the H_(c) of the soft magnetic film, e.g., by at least 2Oe) and to allow high frequency operation of the soft magnetic films inthe internal bias-field mode with minimal magnetic domain wall motion.

The last step 140 in FIG. 1 is to assemble the magnetic thin film withinelectromagnetic devices such as microtransformers, inductors andrecording heads. Step 140 comprises cutting up the substrate (containinga deposited and optionally patterned single layer, multilayer orcomposite-structured magnetic film) into a desirable size, addingappropriate interconnection and conductor circuitry if needed, andassembling within the desired electromagnetic devices.

Shown in FIGS. 4a-b are schematic diagrams illustrating a pot-core typemicrotransformer design comprising the inventive Fe--Cr--N based films.In this design, the multiplicity of soft magnetic film layers 610(laminations with polyimide or other insulating layers therebetween) arefirst deposited, a patterned conductor layer 620 (e.g., containing Culines) is added above magnetic film layers 610, and then more magneticfilm laminations 630 are deposited, as shown.

Shown in FIGS. 5a-b are schematic diagrams illustrating a toroidalmicrotransformer design. Here, a conductor layer 710 in the form ofparallel segments is prepared first, then a Fe--Cr--N based magneticfilm lamination 720 is deposited thereon, and then a top conductor layer730 in the form of parallel segments is added to be connected withsegments of conductor layer 710 to form a toroidal windingconfiguration.

For certain applications, the Fe--Cr--N based films are deposited insuch a way that the easy axis of magnetization coincides with thedirection of applied field from the windings. For very high-frequencyapplications (e.g., approximately 10 MHz or greater), magnetizationswitching by domain wall motion is not desirable and hence themagnetically hard direction is used so that coherent spin rotation modeis operational.

For this reason, in-plane uniaxial magnetic anisotropy and theaccompanying square M-H loop shape is desirable. The uniaxialanisotropy, which is induced, e.g., by thin film deposition in thepresence of magnetic fields, can be defined in terms of an anisotropyfield, H_(k), which is represented by the field in which the hard axismagnetization loop reaches saturation.

Desirable H_(k) values in the inventive films are, e.g., in the rangefrom 10-100 Oe and preferably in the range from 20-50 Oe. Too high of aH_(k) value reduces the high frequency permeability (which isproportional to 4πM/H_(k) in the hard axis operation). Too low of aH_(k) value causes the ferromagnetic resonance frequency to be reducedand interfere with operating frequency ranges. Therefore, too muchmagnetic softness (i.e., a very low H_(k) value) is undesirable for highfrequency devices of this invention.

The "squareness" of the M-H loop in the easy axis direction isdesirable, as the film first can be saturated essentially into a singledomain state along the easy axis, and then operated in a high frequencyalternating current (AC) mode in the hard axis direction to minimize thedomain wall motion. The inventive Fe--Cr--N based films have a"squareness", as defined by the ratio of the remanent magnetization(i.e., M at H=0) to the saturation magnetization, of at least 0.90 andpreferably at least 0.95.

FIGS. 6a-b show embodiments of the invention incorporated intoelectromagnetic devices. A cross-sectional view of a recordingread-write head comprising an embodiment of the inventive film isillustrated in FIG. 6a. The soft magnetic film 810 serves to amplify themagnetic signal from the recorded magnetic memory bit information in themagnetic disk or tape 820 so that the inductive sense coil ormagnetoresistive sensor 830 can generate a higher output signal. Shownalso is the substrate 840.

Alternatively, as shown in FIG. 6b, the inventive film is used as thehigh-magnetization material in the metal-in-gap (MIG) type headconfiguration. In this embodiment, the head 850 is made of, e.g.,ferrite.

It will be apparent to those skilled in the art that many changes andsubstitutions can be made to the thin films and their incorporation intothe electromagnetic devices herein described without departing from thespirit and scope of the invention as defined by the appended claims.

The invention claimed is:
 1. An article, comprising:a non-magneticsubstrate; and a magnetically soft film supported by said non-magneticsubstrate, said magnetically soft film including an alloy ofiron--chromium--nitrogen (Fe--Cr--N) and at least one element selectedfrom the group consisting of titanium (Ti), zirconium (Zr), hafnium(Hf), vanadium (V), molybdenum (Mo), niobium (Nb) and tungsten (W),wherein said alloy contains, by atomic percentage, Cr in the range fromapproximately 0.5% to 20%, N in the range from approximately 1% to 30%,said at least one element selected from the group consisting of Ti, Zr,Hf, V, Mo, Nb and W in the range from approximately 0.1% to 10%, thebalance consisting essentially of Fe, with elements other than Fe, Cr,N, Ti, Zr, Hf, V, Mo, Nb and W being at most approximately 2% wherein atotal, by weight percentage of all elements equals approximately 100%,wherein said article has been heat treated at a temperature of no morethan approximately 150° C.
 2. The article as recited in claim 1, whereinsaid alloy has a composition selected to provide the alloy a coercivity,H_(c), of less than approximately 5.0 oersteds, an anisotropy field,H_(k), in the range from approximately 10 to 100 oersteds, and aremanent magnetization to saturation magnetization ratio of at least0.90.
 3. The article as recited in claim 1, wherein said magneticallysoft film further comprises a plurality of thin film layers and whereinsaid article further comprises a corresponding plurality of dielectricspacer layers formed between said thin film layers in such a way that amultilayer structure is formed.
 4. The article as recited in claim 3,wherein said plurality of dielectric spacer layers further comprisespolyimide.
 5. The article as recited in claim 1, wherein saidmagnetically soft film is formed on said substrate in such a way thatthe average grain structure size of said magnetically soft film is lessthan approximately 500 Å.
 6. The article as recited in claim 1, furthercomprising one or more exchange bias films formed on said magneticallysoft film, said exchange bias films selected from a group consisting ofantiferromagnetic, ferromagnetic and ferrimagnetic material.
 7. Thearticle as recited in claim 1, wherein said article is part of anelectromagnetic device selected from a group consisting of amicrotransformer, an inductor and a magnetic read-write head.
 8. Thearticle as recited in claim 1, wherein said article is for use at anoperating frequency of at least approximately 10 MHz, and wherein saidarticle is saturated along an easy axis of magnetization into a singledomain state and then operated in an alternating current (AC) fieldalong a hard axis of magnetization.